BEWARE of people preaching that we live in special times. People have preached that message before, and those who listened sold their furniture and climbed up on rooftops to await ascension, or built boats to float out the coming flood, or laced up their Nikes and poisoned themselves
in some California subdivision. These prophets are the ones with visions of the
seven-headed beast, with a taste for the hair shirt and the scourge, with twirling eyes. No, better by far to listen to Ecclesiastes, the original wise preacher, jaded after a thousand messiahs and a thousand revivals.

One generation passes away, and another generation comes; but the
earth abides forever.... That which has been is what will be, that which is
done is what will be done, and there is nothing new under the sun. Is there
anything of which it may be said, "See, this is new"? It has already been in
ancient times before us.

And yet, for all that, we may live in a special time. We may live in the strangest, most thoroughly different moment since human beings took up farming, 10,000 years ago, and time more or less commenced. Since then time has flowed in one direction—toward more, which
we have taken to be progress. At first the momentum was gradual, almost
imperceptible, checked by wars and the Dark Ages and plagues and taboos; but in
recent centuries it has accelerated, the curve of every graph steepening like
the Himalayas rising from the Asian steppe. We have climbed quite high. Of
course, fifty years ago one could have said the same thing, and fifty years
before that, and fifty years before that. But in each case it would have
been premature. We've increased the population fourfold in that 150 years; the
amount of food we grow has gone up faster still; the size of our economy has
quite simply exploded.

But now—now may be the special time. So special that in the Western world we
might each of us consider, among many other things, having only one child—that is, reproducing at a rate as low as that at which human beings have ever
voluntarily reproduced. Is this really necessary? Are we finally running up
against some limits?

To try to answer this question, we need to ask another: How many of us will
there be in the near future? Here is a piece of news that may alter the way
we see the planet—an indication that we live at a special moment. At least at first blush the news is hopeful. New demographic evidence shows that it is at least possible that a child born today will live long enough to see the peak of human population.

Around the world people are choosing to have fewer and fewer children—not just in China, where the government forces it on them, but in almost every nation outside the poorest parts of Africa. Population growth rates are lower than they have been at any time since the Second World War. In the past three
decades the average woman in the developing world, excluding China, has gone
from bearing six children to bearing four. Even in Bangladesh the average has
fallen from six to fewer than four; even in the mullahs' Iran it has dropped by
four children. If this keeps up, the population of the world will not quite
double again; United Nations analysts offer as their mid-range projection that
it will top out at 10 to 11 billion, up from just under six billion at the
moment. The world is still growing, at nearly a record pace—we add a New York City every month, almost a Mexico every year, almost an India every decade. But the rate of growth is slowing; it is no longer "exponential," "unstoppable," "inexorable," "unchecked," "cancerous." If current trends hold, the world's population will all but stop growing before the twenty-first century is out.

And that will be none too soon. There is no way we could keep going as we have
been. The increase in human population in the 1990s has exceeded the
total population in 1600. The population has grown more since 1950 than
it did during the previous four million years. The reasons for our recent rapid
growth are pretty clear. Although the Industrial Revolution speeded historical
growth rates considerably, it was really the public-health revolution, and its
spread to the Third World at the end of the Second World War, that set us
galloping. Vaccines and antibiotics came all at once, and right behind came
population. In Sri Lanka in the late 1940s life expectancy was rising at least
a year every twelve months. How much difference did this make? Consider the
United States: if people died throughout this century at the same rate as they
did at its beginning, America's population would be 140 million, not 270
million.

If it is relatively easy to explain why populations grew so fast after the
Second World War, it is much harder to explain why the growth is now slowing.
Experts confidently supply answers, some of them contradictory: "Development is
the best contraceptive"—or education, or the empowerment of women, or hard
times that force families to postpone having children. For each example there
is a counterexample. Ninety-seven percent of women in the Arab sheikhdom of
Oman know about contraception, and yet they average more than six children
apiece. Turks have used contraception at about the same rate as the Japanese,
but their birth rate is twice as high. And so on. It is not AIDS that will slow
population growth, except in a few African countries. It is not horrors like
the civil war in Rwanda, which claimed half a million lives—a loss the planet can make up for in two days. All that matters is how often individual men and women decide that they want to reproduce.

Will the drop continue? It had better. UN mid-range projections assume that
women in the developing world will soon average two children apiece—the rate
at which population growth stabilizes. If fertility remained at current levels,
the population would reach the absurd figure of 296 billion in just 150 years.
Even if it dropped to 2.5 children per woman and then stopped falling, the
population would still reach 28 billion.

But let's trust that this time the demographers have got it right. Let's trust
that we have rounded the turn and we're in the home stretch. Let's trust that
the planet's population really will double only one more time. Even so, this is
a case of good news, bad news. The good news is that we won't grow forever. The
bad news is that there are six billion of us already, a number the world
strains to support. One more near-doubling—four
or five billion more people—will nearly double that strain. Will these be the five billion straws that break the camel's back?

Big Questions

WE'VE answered the question How many of us will there be? But to figure
out how near we are to any limits, we need to ask something else: How big
are we? This is not so simple. Not only do we vary greatly in how much food
and energy and water and minerals we consume, but each of us varies over time.
William Catton, who was a sociologist at Washington State University before his
retirement, once tried to calculate the amount of energy human beings use each
day. In hunter-gatherer times it was about 2,500 calories, all of it food. That
is the daily energy intake of a common dolphin. A modern human being uses
31,000 calories a day, most of it in the form of fossil fuel. That is the
intake of a pilot whale. And the average American uses six times that—as much as a sperm whale. We have become, in other words, different from the people we used to be. Not kinder or unkinder, not deeper or stupider—our natures seem to have changed little since Homer. We've just gotten bigger. We appear to be the same species, with stomachs of the same size, but we aren't. It's as if each of us were trailing a big Macy's-parade balloon around, feeding it constantly.

So it doesn't do much good to stare idly out the window of your 737 as you fly
from New York to Los Angeles and see that there's plenty of empty space
down there. Sure enough, you could crowd lots more people into the nation or
onto the planet. The entire world population could fit into Texas, and each
person could have an area equal to the floor space of a typical U.S. home. If
people were willing to stand, everyone on earth could fit comfortably into half
of Rhode Island. Holland is crowded and is doing just fine.

But this ignores the balloons above our heads, our hungry shadow selves, our
sperm-whale appetites. As soon as we started farming, we started setting aside
extra land to support ourselves. Now each of us needs not only a little plot of
cropland and a little pasture for the meat we eat but also a little forest for
timber and paper, a little mine, a little oil well. Giants have big feet. Some
scientists in Vancouver tried to calculate one such "footprint" and found that
although 1.7 million people lived on a million acres surrounding their city,
those people required 21.5 million acres of land to support them—wheat fields in Alberta, oil fields in Saudi Arabia, tomato fields in California. People in Manhattan are as dependent on faraway resources as people on the Mir space station.

Those balloons above our heads can shrink or grow, depending on how we choose
to live. All over the earth people who were once tiny are suddenly growing like
Alice when she ate the cake. In China per capita income has doubled since the
early 1980s. People there, though still Lilliputian in comparison with us, are
twice their former size. They eat much higher on the food chain,
understandably, than they used to: China slaughters more pigs than any other
nation, and it takes four pounds of grain to produce one pound of pork. When, a
decade ago, the United Nations examined sustainable development, it issued a
report saying that the economies of the developing countries needed to be five
to ten times as large to move poor people to an acceptable standard of
living—with all that this would mean in terms of demands on oil wells and
forests.

That sounds almost impossible. For the moment, though, let's not pass judgment.
We're still just doing math. There are going to be lots of us. We're going to
be big. But lots of us in relation to what? Big in relation to what? It could
be that compared with the world we inhabit, we're still scarce and small. Or
not. So now we need to consider a third question: How big is the
earth?

ANY state wildlife biologist can tell you how many deer a given area can
support—how much browse there is for the deer to eat before they begin to
suppress the reproduction of trees, before they begin to starve in the winter.
He can calculate how many wolves a given area can support too, in part by
counting the number of deer. And so on, up and down the food chain. It's not an
exact science, but it comes pretty close—at least compared with figuring out
the carrying capacity of the earth for human beings, which is an art so dark
that anyone with any sense stays away from it.

Consider the difficulties. Human beings, unlike deer, can eat almost anything
and live at almost any level they choose. Hunter-gatherers used 2,500 calories
of energy a day, whereas modern Americans use seventy-five times that. Human
beings, unlike deer, can import what they need from thousands of miles away.
And human beings, unlike deer, can figure out new ways to do old things. If,
like deer, we needed to browse on conifers to survive, we could
crossbreed lush new strains, chop down competing trees, irrigate forests, spray
a thousand chemicals, freeze or dry the tender buds at the peak of harvest,
genetically engineer new strains—and advertise the merits of maple buds until everyone was ready to switch. The variables are so great that professional demographers rarely even bother trying to figure out carrying capacity. The demographer Joel Cohen, in his potent book How Many People Can the Earth Support? (1995), reports that at two recent meetings of the Population Association of America exactly none of the more than 200 symposia dealt with carrying capacity.

But the difficulty hasn't stopped other thinkers. This is, after all, as big a
question as the world offers. Plato, Euripides, and Polybius all worried that
we would run out of food if the population kept growing; for centuries a steady
stream of economists, environmentalists, and zealots and cranks of all sorts
have made it their business to issue estimates either dire or benign. The most
famous, of course, came from the Reverend Thomas Malthus. Writing in 1798, he
proposed that the growth of population, being "geometric," would soon outstrip
the supply of food. Though he changed his mind and rewrote his famous essay,
it's the original version that people have remembered—and lambasted—ever since. Few other writers have found critics in as many corners. Not only have
conservatives made Malthus's name a byword for ludicrous alarmism, but Karl
Marx called his essay "a libel on the human race," Friedrich Engels believed
that "we are forever secure from the fear of overpopulation," and even Mao
Zedong attacked Malthus by name, adding, "Of all things in the world people are
the most precious."

Each new generation of Malthusians has made new predictions that the end was
near, and has been proved wrong. The late 1960s saw an upsurge of Malthusian
panic. In 1967 William and Paul Paddock published a book called
Famine—1975!, which contained a triage list: "Egypt: Can't-be-saved.... Tunisia: Should Receive Food.... India: Can't-be-saved."
Almost simultaneously Paul Ehrlich wrote, in his best-selling The Population Bomb (1968), "The battle to feed all of humanity is over. In the 1970s, the world will undergo famines—hundreds of millions of people will starve to death." It all seemed so certain, so firmly in keeping with a world soon to be darkened by the first oil crisis.

But that's not how it worked out. India fed herself. The United States still
ships surplus grain around the world. As the astute Harvard social scientist
Amartya Sen points out, "Not only is food generally much cheaper to buy today,
in constant dollars, than it was in Malthus's time, but it also has become
cheaper during recent decades." So far, in other words, the world has more or
less supported us. Too many people starve (60 percent of children in South Asia
are stunted by malnutrition), but both the total number and the percentage have
dropped in recent decades, thanks mainly to the successes of the Green
Revolution. Food production has tripled since the Second World War, outpacing
even population growth. We may be giants, but we are clever giants.

So Malthus was wrong. Over and over again he was wrong. No other prophet has
ever been proved wrong so many times. At the moment, his stock is especially
low. One group of technological optimists now believes that people will
continue to improve their standard of living precisely because they
increase their numbers. This group's intellectual fountainhead is a brilliant
Danish economist named Ester Boserup—a sort of anti-Malthus,
who in 1965 argued that the gloomy cleric had it backward. The more people,
Boserup said, the more progress. Take agriculture as an example: the first
farmers, she pointed out, were slash-and-burn cultivators, who might farm a
plot for a year or two and then move on, not returning for maybe two decades.
As the population grew, however, they had to return more frequently to the same
plot. That meant problems: compacted, depleted, weedy soils. But those new
problems meant new solutions: hoes, manure, compost, crop rotation, irrigation.
Even in this century, Boserup said, necessity-induced
invention has meant that "intensive systems of agriculture replaced extensive
systems," accelerating the rate of food production.

Boserup's closely argued examples have inspired a less cautious group of
popularizers, who point out that standards of living have risen all over the
world even as population has grown. The most important benefit, in fact, that
population growth bestows on an economy is to increase the stock of useful
knowledge, insisted Julian Simon, the best known of the so-called cornucopians,
who died earlier this year. We might run out of copper, but who cares? The mere
fact of shortage will lead someone to invent a substitute. "The main fuel to
speed our progress is our stock of knowledge, and the brake is our lack of
imagination," Simon wrote. "The ultimate resource is people—skilled, spirited, and hopeful people who will exert their wills and imaginations for their own benefit, and so, inevitably, for the benefit of us all."

Simon and his ilk owe their success to this: they have been right so far. The
world has behaved as they predicted. India hasn't starved. Food is cheap. But
Malthus never goes away. The idea that we might grow too big can be disproved
only for the moment—never for good. We might always be on the threshold of a
special time, when the mechanisms described by Boserup and Simon stop working.
It is true that Malthus was wrong when the population doubled from 750 million
to 1.5 billion. It is true that Malthus was wrong when the population doubled
from 1.5 billion to three billion. It is true that Malthus was wrong when the
population doubled from three billion to six billion. Will Malthus still be
wrong fifty years from now?